This invention relates to a centrifugally cast pipe comprised of bulk polymerized polymers.
It is conventional to centrifugally cast thermosetting and thermoplastic resins to form pipes of diameters within the range of 1-12 inches. See U.S. Pat. Nos. 3,988,412, 3,816,582, 3,718,161 and 2,887,728. The pipes formed are generally of a thickness wherein reinforcement with fibers such as fiber glass is desired.
While the pipes obtained from these resins have been satisfactory, the resins used have placed limitations on the processing and the products obtained from centrifugal casting. The viscosity of the resins used has limited the dimensions of the pipe in that spinning large cylindrical shapes becomes more difficult as the viscosity of the resin increases. The wall thickness of the pipes is often limited due to the long cure times of thermosetting resins. Tennyson, U.S. Pat. No. 3,816,582, describes casting times of 6-7 hours for a wall thickness of about 0.050 inch when at room temperature. This cure time can be reduced if higher temperatures are utilized. Fiber reinforcements are often necessary to provide the desired strength and prevent cracking of unreinforced polymers. These fiber reinforcements tend to provide a "wick" for some corrosive materials, allowing the corrosive material to penetrate the surface causing damage not only to the immediate surface but to the subsurface as well.
Polymers obtained by the bulk polymerization of monomers in the absence of solvent are well known. See U.S. Pat. Nos. 4,426,502, 4,380,617 and 4,689,380. The reactive monomer formulations from which these polymers are derived are very low in viscosity, allowing easy transport into molds and other processing equipment. The reactive monomer formulations used in bulk polymerization techniques typically polymerize very rapidly, allowing short cycle times when molding parts within a closed mold. While the use of bulk polymerized polymers does present advantages to centrifugally cast plastic pipe, acceptable pipes have not yet been obtained. The high reactivity makes it difficult for the reactive monomer formulation to obtain a cylindrical shape within the mold prior to gelation. Reactive monomer formulations with delayed gel times do provide adequate time to fill the mold; however, this delay in gel time allows entrapped gas bubbles to coalesce forming imperfections on the inner surface, particularly where the reactive monomer formulation generates a gas during cure.